Angularly selective attenuation of light transmission artifacts in wearable displays
A wearable display system includes an eyepiece stack having a world side and a user side opposite the world side. During use, a user positioned on the user side views displayed images delivered by the wearable display system via the eyepiece stack which augment the user's field of view of the user's environment. The system also includes an optical attenuator arranged on the world side of the of the eyepiece stack, the optical attenuator having a layer of a birefringent material having a plurality of domains each having a principal optic axis oriented in a corresponding direction different from the direction of other domains. Each domain of the optical attenuator reduces transmission of visible light incident on the optical attenuator for a corresponding different range of angles of incidence.
1. A method, comprising:
displaying images to a user via an eyepiece stack of a wearable display system to augment the user's field of view of the user's environment;
attenuating transmission of ambient light from the user's environment through the eyepiece stack to the user while displaying the images, the attenuating comprising:
polarizing the ambient light incident on the eyepiece stack to provide polarized ambient light;
using a spatially-varying o-plate having a plurality of domains each having a principal optic axis oriented in a corresponding direction different from the direction of other domains, rotating a polarization state of the polarized ambient light by an amount related to the incident angle of the polarized ambient light and the domain at which the polarized ambient light is incident, the rotating providing polarization-rotated ambient light; and
absorbing at least a portion of the polarization-rotated ambient light to provide attenuated ambient light, an amount of absorption varying depending on an incident angle of the polarization-rotated polarized ambient light and the domain at which the corresponding polarized ambient light is incident; and
combining the attenuated ambient light with light forming the displayed images to provide the augmented field of view of the user's environment.
2. The method of claim 1 , wherein, at a domain intersecting a viewing axis of the wearable display, the polarization state of the polarized ambient light is rotated by zero degrees, and, at least one domain away from the viewing axis, the polarization state of the polarized ambient light is rotated by an amount greater than zero.
3. The method of claim 2 , wherein rotating the polarization state of the polarized ambient light comprises rotating the polarization state by an amount in a polar coordinate direction and rotating the polarization state by an amount in an azimuthal direction.
4. The method of claim 3 , wherein, for at least two domains in which the polarization state of the polarized ambient light is rotated by a nonzero amount, the amount the polarization state is rotated in the polar coordinate direction is different than the amount the polarization state is rotated in the azimuthal direction.
5. The method of claim 1 , wherein the plurality of domains comprises domains arranged in a one dimensional pattern, or a two dimensional pattern.
6. The method of claim 1 , wherein polarizing the ambient light comprises linearly polarizing the ambient light along a first pass axis.
7. The method of claim 6 , wherein absorbing at least the portion of the polarization-rotated ambient light comprises using a linear polarizer having a pass axis that is crossed from the first pass axis.
8. The method of claim 6 , wherein polarizing the ambient light further comprises circularly polarizing the ambient light and, prior to absorbing, circularly polarizing the polarization-rotated ambient light.
9. The method of claim 8 , wherein the amount by which the polarization state of the ambient light is rotated varies depending on an angle of incidence of light incident on the eyepiece stack.
10. The method of claim 9 , wherein light having large angles of incidence is rotated less than light having small angles of incidence.
11. The method of claim 1 , further comprising, using a second layer of a birefringent material having a second plurality of domains each having a principal optic axis oriented in a corresponding direction different from the direction of other domains, rotating a polarization state of the polarization-rotated ambient light by an amount related to the incident angle of the polarization-rotated ambient light and the domain at which the polarization-rotated ambient light is incident, the rotating providing twice-polarization-rotated ambient light, and absorbing at least a portion of the twice-polarization-rotated ambient light to provide the attenuated ambient light.
12. The method of claim 11 , further comprising, between the first rotating and the second rotating, linearly polarizing the polarization-rotated ambient light.
13. The method of claim 1 , wherein for an aperture of the eyepiece stack corresponding to an eyebox of the wearable display, a white point of images viewed through the eyepiece stack on a user side with a D65 illuminant on a world side varies by 0.01 Δu′v′ or less in a CIELUV color space for incident angles of 40° or less across an aperture of the eyepiece stack defining the eyebox.
14. The method of claim 13 , wherein the aperture has a diameter in a range from 20 mm to 50 mm.